The invention relates to continuously renewing separators having a cylindrical revolving wall of the type comprising a helicoidal winding with closely adjacent turns of an endless belt which is looped about itself so as to unwind slowly at one end and rewind at the other end while advancing axially at the same time as it is drawn into continuous rotation at a greater speed.
According to German patent No. 691,923, this type of centrifuge is known in which the endless belt is a flat perforated band, the helicoidal winding being disposed inside a rotating cage whose bars turn about themselves, the renewing entrainment of the band being insured by the return loop proper which passes through the inside of the cylindrical winding and winds onto a central capstan which is coaxial with the cage. Drive of this band is thus insured both by friction and by traction of the return side, which is a serious disadvantage in that it does not allow a correct drive. In fact, in the principal cylindrical winding, the band traction from the inside is transmitted unsatisfactorily since this winding is supported on the inside by the cage equipped with rotating bars. However, it is inappropriate to provide rotating bars in the interior because they will interfere with centrifuged solid products.
Important progress has been achieved by French patent No. 2 372 658, or European Patent No. 0 000 004 with regard to the type of drive of the endless band. Here, the drive is insured again by friction, but also by direct action on the cylindrical part which is achieved by entraining the bars directly into rotation by an appropriate mechanism, adherence being achieved quite naturally by the centrifugal force. In this case, no action is exerted on the return loop which thus can be a natural free loop of any trajectory, for example, outside the cylindrical wall. Another important progress also achieved by the above mentioned prior patent, comprises replacing the flat perforated band by a solid belt without perforations and which is chamfered, non-wraping and easy to clean. However, this device requires a reducer with multiple outlets, and the rotating bars which are of small diameter and great length are subjected to alternate rotational deflection because of the centrifugal force which limits the maximum speed at which the device can rotate. Further, serious problems may arise from the point of view of expansion when the belt is made of a material which expands more than does the cage and when the apparatus functions under heat conditions, for example in the treatment of coffee. In fact, in this case the winding with closely adjacent turns totals a great length of belt, and the accumulated differential expansion of this belt in relation to the cage is reflected exclusively in the return loop which thus undergoes substantial variations. The latter are tolerated by the free mounting of this loop, as explained above, but they cause considerable obstruction of the rotating assembly and are an additional reason for limiting the speed under heat conditions.